title: Dynamic interactions of gas exchange, body mass, and progressive exercise in children.
abstract: OBJECTIVE
  Cardiopulmonary exercise testing (CPET) is increasingly used as a biomarker of fitness in children. Maximal or peak values remain the most common variables obtained in CPET, but these physiologically challenging high-intensity work rates (WR) are often not achieved. We hypothesized that interactions of gas exchange, heart rate (HR), and WR CPET variables (slopes) could yield useful mechanistic and clinical insights that might enhance the clinical utility of CPET in children. We further hypothesized that the dependence of the slope on body mass could be predicted by the first-principle analysis of body size and physiological response.
  
  
  METHODS
  One hundred and sixty-nine healthy participants (8-18 yr old, body mass index <95th percentile, 82 females) underwent dual x-ray absorptiometry scan to estimate lean body mass (LBM) and performed a ramp-type progressive cycle ergometry exercise protocol with a breath-by-breath measurement of gas exchange. Linear regression was used to calculate the slopes among VO2, VCO2, VE, HR, and WR.
  
  
  RESULTS
  ΔWR/ΔHR (r = 0.87) and ΔVO2/ΔHR (r = 0.96) were strongly correlated with VO2peak, whereas ΔVO2/ΔWR (r = 0.42) and ΔVE/ΔVCO2 (r = -0.51) were mildly correlated with peak values. LBM was more highly correlated with those slopes predicted to be body size dependent (P < 0.0001) compared with total body mass.
  
  
  CONCLUSIONS
  The data largely supported our original hypotheses. Unlike peak or maximal values, which are derived from no more than a few data points at the end of a progressive exercise test, the CPET slopes were calculated from a much larger data set obtained throughout the test. An analysis of these slopes might ultimately prove useful clinically and in research studies when peak values are not achieved.
authors.affiliation: Department of Pediatrics, Pediatric Exercise Research Center, University of California, Irvine, CA.
authors.forename: Dan M
authors.initials: DM
authors.lastname: Cooper
authors.forename: Szu-Yun
authors.initials: SY
authors.lastname: Leu
authors.forename: Pietro
authors.initials: P
authors.lastname: Galassetti
authors.forename: Shlomit
authors.initials: S
authors.lastname: Radom-Aizik
mesh_terms: D000293:Adolescent; D000367:Age Factors; D015992:Body Mass Index; D049628:Body Size; D002648:Child; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D010100:Oxygen / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D012737:Sex Factors
chemical_list: D010100:Oxygen